Conventionally, a printed wiring board in which a solder resist pattern which is a patterned solder resist film is formed on a substrate having a wiring provided on its top face is widely used. As electronic devices become smaller and densified, a still finer solder resist pattern is demanded in a printed wiring board.
As a method for forming a fine solder resist pattern, a method of applying a composition for solder resist by an inkjet method is proposed. In the inkjet method, the number of steps is reduced in comparison with the case of forming a solder resist pattern by a screen printing method. Therefore, in the inkjet method, it is possible to form a solder resist pattern easily and efficiently.
In the case of applying a composition for solder resist by an inkjet method, the composition is required to have a somewhat low viscosity at the time of application. On the other hand, an inkjet device capable of printing while being warmed at 50° C. or higher is developed. By warming a composition for solder resist to 50° C. or higher in the inkjet device, the composition for solder resist get relatively low viscosity, and dischargeability of the composition for solder resist by the inkjet device would be further improved.
Further, a composition for solder resist that can be applied by an inkjet method is disclosed in the following Patent document 1. In the following Patent Document 1, a curable composition for inkjet including a monomer having a (meth)acryloyl group and a heat-curable functional group, a photoreactive diluent having a weight average molecular weight of 700 or less, and a photopolymerization initiator is disclosed. The curable composition for inkjet has a viscosity at 25° C. of 150 mPa·s or less.